This is a revision of a proposal to continue support to study various aspects of the biochemistry of the transglutaminases, factor XIII and tissue transglutaminase. The aim is to determine structural features that govern the stability of these proteins and to understand the various intermolecular associations that regulate their functions. The proposal contains four Specific Aims: 1)control mechanisms operating i fibrin stabilization, 2)enzyme mechanistic studies on FXIIIA , 3) identification of donor sites in the 2 chains of human fibrin(ogen) reacting with Factor XIIIa, and 4) further identification of binding domains involved in the interaction of transglutaminase to human plasma fibronectin.